The objective of this Physician Scientist Award application is to provide the applicant lwith the training needed to pursue an academic career in the field of Hepatology. The techniques of protein chemistry, cell biology, and molecular genetics will be used to study the molecular organization of the tight junction and its role in the pathogenesis of cholestasis. In phase 1, under the co-sponsorship of Drs. James Anderson and Jon Morrow and a basic science advisory committee, the applicant will use cDNA sequence data from zonula occludens-1 (ZO-1), the first tight junction specific protein identified, to characterize the structural and functional properties of ZO-1, investigate the biologic significance of ZO-1 mRNA alternate splicing and to identify additional tight junction proteins. A combination of fusion protein production, transfection experiments and RNA analysis will be used in this work. In phase 2, under the continued sponsorship of Dr. James Anderson and a clinical advisory committee, the applicant will use information gained about the molecular nature and organization of the tight junction to study animal models of cholestasis where tight junction structure and function are known to be altered. These studies are expected to yield valuable information about the mechanisms of the paracellular contribution to cholestasis and to be broadly applicable to other developmental and pathologic conditions where epithelial and endothelial paracellular permeability are altered.